The targeted stimulation of arteriogenesis, which is defined as the formation and lumenal expansion of the arterioles and arteries, is a promising treatment for ischemia caused by occlusive vascular disease. To date, attempts at creating therapeutic arteriogenesis have centered on the delivery of selected growth factor genes and proteins: Recently, we have developed an innovative new technique, based on contrast agent microbubble destruction with ultrasound, for stimulating arteriogenesis in and around regions of ischemia. This arteriogenic response, which may be targeted to selected tissue regions using the ultrasound beam, is accompanied by an increase in hyperemic capacity in the treated tissue, thereby demonstrating the potential of this technique for restoring blood flow to organs affected by arterial occlusion. In the clinical setting, this method has the potential to be performed with minimal invasiveness. This proposal consists of 4 specific aims that broadly address the clinical potential of the ultrasound- microbubble technique for enhancing blood flow and the rational manipulation of the technique for amplifying and potentially prolonging arteriogenesis. The first and second specific aims will respectively test the efficacy of ultrasonic microbubble destruction for enhancing blood flow to muscle that is chronically affected by vascular occlusion and establish which microvascular remodeling events create the flow enhancement. Studies for the third specific aim will determine how arteriogenesis and flow restoration can be controlled through alterations in user-controlled factors, namely microbubble size, microbubble dosage, ultrasound frequency, and application time. With this information, we will then develop an optimized protocol for generating arteriogenesis at a clinically relevant microbubble dosage. In the fourth specific aim, we will deliver polyethylenimine (PEI) nanocomplexes bearing genes for either a pro-arteriogenic growth factor (bFGF) or a pro-arteriogenic cytokine (MCP-1) to the arterially occluded muscle. These final studies will combine a state-of-the-art approach for cell transfection with an ultrasound targeted delivery strategy, with the goal of rationally manipulating the magnitude and longevity of the arteriogenesis response. Given the broad applicability of this targeted gene delivery method, it is likely these studies will have a significant impact on the investigation and treatment of many other pathologies and conditions.